首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2639篇
  免费   93篇
  国内免费   23篇
化学   1644篇
晶体学   8篇
力学   60篇
数学   423篇
物理学   620篇
  2023年   10篇
  2022年   27篇
  2021年   31篇
  2020年   42篇
  2019年   29篇
  2018年   35篇
  2017年   39篇
  2016年   72篇
  2015年   64篇
  2014年   69篇
  2013年   133篇
  2012年   199篇
  2011年   196篇
  2010年   138篇
  2009年   114篇
  2008年   177篇
  2007年   177篇
  2006年   180篇
  2005年   216篇
  2004年   146篇
  2003年   132篇
  2002年   120篇
  2001年   22篇
  2000年   25篇
  1999年   21篇
  1998年   22篇
  1997年   18篇
  1996年   40篇
  1995年   19篇
  1994年   18篇
  1993年   25篇
  1992年   13篇
  1991年   7篇
  1990年   9篇
  1989年   15篇
  1988年   9篇
  1987年   8篇
  1986年   11篇
  1985年   15篇
  1984年   15篇
  1983年   12篇
  1982年   11篇
  1981年   11篇
  1980年   5篇
  1979年   10篇
  1976年   6篇
  1973年   7篇
  1972年   5篇
  1970年   4篇
  1968年   4篇
排序方式: 共有2755条查询结果,搜索用时 15 毫秒
11.
12.
The multivariate model, where not only parameters of the mean value of the observation matrix, but also some other parameters occur in constraints, is considered in the paper. Some basic inference is presented under the condition that the covariance matrix is either unknown, or partially unknown, or known. Supported by the grant of the Council of Czech Republic MSM 6 198 959 214.  相似文献   
13.
We study the branching ratio, CP-violating asymmetry, forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the exclusive decay B → Kτ+τ in the two Higgs doublet model with tree level flavor changing neutral currents (model III). We analyse the dependencies of these quantities on the neutral Higgs boson contributions and the CP parameter sinθ in the model III. We observe that to determine the neutral Higgs boson effects, the measurements of the forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the decay B → Kτ+τ are promising.  相似文献   
14.
15.
One possible natural monotone version of countable paracompactness, MCP, turns out to have some interesting properties. We investigate various other possible monotone versions of countable paracompactness and how they are related.  相似文献   
16.
It is well known that S 12 cannot prove the injective weak pigeonhole principle for polynomial time functions unless RSA is insecure. In this note we investigate the provability of the surjective (dual) weak pigeonhole principle in S 12 for provably weaker function classes. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
17.
18.
This paper explores the differences between real and complex microcontinuity for hyperreal polynomials, with hypernatural degree and nonstandard coefficients. On the real line, complex microcontinuity differs from real microcontinuity in replacing the coefficients with their absolute values. Apart from this feature, not much analogy is found between (absolute) convergence of series and (absolute) microcontinuity of infinite polynomials, even if these are infinite partial sums of a standard series. Real microcontinuity may be confined to isolated monalds, whereas complex microcontinuity always propagates a noninfinitesimal distance. An infinite partial sum of a power series can be microcontinuous outside the circle of convergence.  相似文献   
19.
Resonant-cavity-enhanced photodetectors and LEDs in the mid-infrared   总被引:1,自引:0,他引:1  
In this paper we outline the use of resonant-cavity enhancement for increasing the exterior coupling efficiency of photodetectors and light-emitting diodes (LEDs) in the mid-infrared (MIR) spectral region. This method is potentially very important in the MIR because encapsulation is not presently feasible due to the lack of suitable materials. Among other potential applications, resonant-cavity-enhanced (RCE) photodetectors and LEDs could be particularly suitable for greenhouse gas detection because of their ‘pre-tunable’ spectrally narrowed resonantly enhanced peaks. We also present the optical characterization of an InAs RCE photodetector aimed at the detection of methane gas (λ≈3.3 μm), and an InAs/InAs0.91Sb0.09 resonant-cavity LED (RCLED) aimed at carbon dioxide gas (λ≈4.2 μm). The high peak responsivity of the RCE photodetector was 34.7 A/W at λ=3.14 μm, and the RCLED peaked at λ=3.96 μm. These are among the longest operating wavelengths for III–V RCE photodetectors and RCLEDs reported in the literature.  相似文献   
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号